The purpose of this study is to determine the effects of a walking exercise program on management of fatigue during breast cancer treatment. The study is a randomized, controlled clinical trial design, stratified by type of medical treatment: radiotherapy, adjuvant chemotherapy, or combined modalities. Four university teaching hospitals with National Cancer Institute designed Cancer Centers and one community cancer center comprise the clinical research settings. The sample consists of newly diagnosed Stage I-III breast cancer patients who have completed surgical treatment and are beginning primary radiotherapy or adjuvant cytotoxic chemotherapy or combinations of both. Following random assignment, subjects in the exercise group will be prescribed an individualized, self-paced, home-based walking exercise program that they will maintain throughout their cancer treatment. Subjects in the control group will receive the usual care given during breast cancer treatment (no prescribed walking program). Symptoms and response to treatment will be assessed at the beginning, middle and end of either therapy. Groups will be compared by statistical analysis. The independent variable is participation in a walking exercise program. The primary dependent variable is fatigue level; additional variables are physical functioning, emotional distress, difficulty sleeping, weight gain, and quality of life. The out-of-pocket costs of cancer care and its relationship to unmanaged symptoms will also be investigated.